Optical measurement system for obtaining and analyzing surface topography of object
An optical measurement system comprises a polarization beam splitter for dividing an incident beam into a reference beam and a measurement beam, a first beam splitter for reflecting the measurement beam to form a first reflected measurement beam, a spatial light modulator for modulating the first reflected measurement beam to form a modulated measurement beam, a condenser lens for focusing the modulated measurement beam to an object to form a penetrating measurement beam, an objective lens for converting the penetrating measurement beam into a parallel measurement beam, a mirror for reflecting the parallel measurement beam to form an object beam, a second beam splitter for reflecting the reference beam to a path coincident with that of the object beam, and a camera for receiving an interference signal generated by the reference beam and the object beam to generate an image of the object.
1. An optical measurement system, comprising:
a polarization beam splitter, dividing an incident beam into a reference beam and an original measurement beam;
a first beam splitter, receiving the original measurement beam and reflecting the original measurement beam to form a first reflected measurement beam;
a spatial light modulator, receiving the first reflected measurement beam and modulating a reflection direction of the first reflected measurement beam to form a modulated measurement beam;
a condenser lens, receiving the modulated measurement beam and focusing the modulated measurement beam to an object to be measured, wherein the modulated measurement beam penetrates the object to be measured to form a penetrating measurement beam;
an objective lens, receiving the penetrating measurement beam and converting the penetrating measurement beam into a parallel measurement beam;
a mirror, receiving the parallel measurement beam and reflecting the parallel measurement beam to form a second reflected measurement beam;
a second beam splitter, receiving the reference beam and reflecting the reference beam to a path coincident with a path of the second reflected measurement beam, wherein the reference beam interferes with the second reflected measurement beam to generate an interference signal;
a camera, receiving the interference signal to generate an original image, wherein the original image comprises a phase distribution image having surface topography representative of the object to be measured; and
a processing device, connected with the camera, wherein the processing device comprises an image processor, and the image processor obtains the phase distribution image using a field retrieval algorithm, and obtains a three-dimensional image of refractive index distribution of the object to be measured using information represented by the phase distribution image,
wherein the processing device comprises a classifier performing a classification procedure, and the classification procedure comprises:
obtaining three-dimensional images of samples, wherein the three-dimensional images respectively represent refractive index distribution of the samples;
obtaining pieces of reference original data respectively from the three-dimensional images, wherein each of the pieces of reference original data represents structural features of a corresponding one of the samples;
dividing the pieces of reference original data into a training data set and a test data set;
training the training data set;
establishing one of multiple reference classification models by combining feature subsets extracted from the training data set;
choosing a best classification model from the multiple reference classification models; and
applying the best classification model for determining a type of the object to be measured.
2. The optical measurement system according to claim 1 , wherein the information presented by the phase distribution image and the three-dimensional image satisfy an equation, wherein the equation is:
U
Rytov
(
f
x
,
f
y
,
z
+
=
0
)
=
1
j
4
π
fz
(
F
x
,
F
y
,
F
z
)
;
wherein U Rytov (f x , f y , z + =0) represents the three-dimensional image, and (F r , F y , F z ) represents the information represented by the phase distribution image.
3. The optical measurement system according to claim 1 , wherein
each of the pieces of reference original data further represents biochemical characteristics of the corresponding one of the samples.
4. The optical measurement system according to claim 3 , wherein the step of obtaining the pieces of reference original data in the classification procedure comprises:
according to voxel data of each of the three-dimensional images, obtaining a surface area and a volume of a corresponding one of the samples to represent the structural features; and
based on local concentration of non-aqueous molecules of the samples, determining protein density and dry mass of each of the samples to represent the biochemical characteristics.
5. The optical measurement system according to claim 4 , wherein the step of obtaining the pieces of reference original data in the classification procedure further comprises:
determining sphericity of each of the samples by a ratio of the volume to the surface area when the samples are substantially spherical.
6. The optical measurement system according to claim 3 , wherein the step of training the training data set in the classification procedure performed by the classifier is performed by using a K-nearest neighbors algorithm.
7. The optical measurement system according to claim 3 , wherein the step of choosing the best classification model in the classification procedure performed by the classifier is performed by performing a cross-validation.
8. The optical measurement system according to claim 7 , wherein the cross-validation comprises a leave-one-out cross-validation.
9. The optical measurement system according to claim 1 , wherein the step of obtaining the pieces of reference original data in the classification procedure comprises:
according to voxel data of each of the three-dimensional images, obtaining a surface area and a volume of a corresponding one of the samples to represent the structural features.
10. The optical measurement system according to claim 1 , wherein the step of training the training data set in the classification procedure performed by the classifier is performed by using a K-nearest neighbors algorithm.
11. The optical measurement system according to claim 1 , wherein the step of choosing the best classification model in the classification procedure performed by the classifier is performed by performing a cross-validation.
12. The optical measurement system according to claim 11 , wherein the cross-validation comprises a leave-one-out cross-validation.
13. The optical measurement system according to claim 1 , further comprising:
a spatial filter, disposed on a path of the incident beam to the polarization beam splitter for filtering out spatial noise of the incident beam; and
a half-wavelength plate, disposed on the path of the incident beam to the polarization beam splitter for rotating a polarization direction of the incident beam in which the spatial noise is filtered out by π/2.
14. The optical measurement system according to claim 1 , further comprising:
a half-wavelength plate, disposed on a path of the incident beam to the polarization beam splitter for rotating a polarization direction of the incident beam by π/2.
15. The optical measurement system according to claim 14 , further comprising:
a half-wavelength plate, disposed on a path of the reference beam to the second beam splitter for rotating a polarization direction of the reference beam reflected by the second beam splitter to be the same as a polarization direction of the second reflected measurement beam after penetrating the second beam splitter.
16. The optical measurement system according to claim 1 , wherein the spatial light modulator is a digital micro-mirror device used in digital light processing (DLP).
17. The optical measurement system according to claim 1 , wherein the spatial light modulator is a liquid crystal on silicon.
18. The optical measurement system according to claim 1 , wherein intensity of the reference beam is approximately equal to intensity of the modulated measurement beam.